The present invention relates to processes for the underground gasification of coal, of the kind in which a gasifying agent is ducted through a bore, to be ejected in situ in the direction of a seam of coal, from which is extracted a fuel gas resulting from an incomplete combustion of the said coal, said fuel gas being ducted to the surface while flowing in counterflow and around said jet of gasifying agent and then being ducted to the surface via said bore.
It is known that there is thus assured the formation of a fuel gas commonly containing at least carbon monoxide, and very variable quantities of methane. The interest inherent in this process is that it utilizes a single bore only for the products fed in and the fuel drawn off, but the problem thus presented is to avoid any complementary combustion reaction between the gasifying agent and the fuel gas resulting from the incomplete combustion and, to this end, the methods hitherto used consisted either in constantly causing forward feed of the head supplying the gasifying agent until it reached the direct vicinity of the coal face at which the combustion takes place, which produces disadvantages regarding control and thermal shock, or in diluting the gasifying agent within expelled protective capsules flowing by gravity towards the combustion face.
It is an object of the invention to simplify the means applied to provide in situ gasification of coal, in particular found at very great depth, by considerably simplifying the means applied and by providing a precise check on the incomplete combustion phenomenon.